1. Field of the Invention
The present invention relates in general to a catalytic converter arrangement of an automotive exhaust system, and more particularly to a catalytic converter arrangement in which an electrically-heatable metal catalyst support is incorporated.
2. Description of the Prior Art
A catalytic converter is incorporated into an automotive exhaust system for transforming noxious emissions such as CO, HC and NO.sub.x into harmless gases such as CO.sub.2, N.sub.2 and H.sub.2 O.
When a catalytic converter is positioned in an engine room or compartment and immediately downstream from an engine exhaust manifold, a catalyst support of the catalytic converter is easily heated, due to the heated emission from the exhaust manifold, up to an operating temperature where a catalyst coated on the catalyst support begins catalytic activity. However, due to a limited space of the engine room, the catalytic converter positioned in the engine room is not in general permitted to be so sized as to fully clean up noxious emissions. Therefore, there is provided another catalytic converter below an automotive body for supplementing the catalytic converter in the engine room.
Both of their above-mentioned catalytic converters are not heated up to the operating temperatures within a short time after the engine has been started. Therefore, in some automobiles, the catalytic converter in the engine room has an electrically-heatable metal catalyst support for rapidly increasing the temperature of the catalyst support up to its operating temperature. One such type of catalytic converter arrangement has a first catalytic converter which is positioned in the engine room and immediately downstream from the engine exhaust manifold, and a second catalytic converter which is positioned below the automotive body. The first catalytic converter has an upstream portion which has an electrically-heatable metal catalyst support, and a downstream portion which has a ceramic catalyst support. However, this conventional catalytic converter arrangement has the following drawback.
Since the metal catalyst support of the first catalytic converter is positioned immediately downstream from the exhaust manifold, it tends to be overheated after the engine has been warmed up. With this, durability of the first catalytic converter is shortened.